Embedding Polyphenols Extract from Grape Marc into Inorganic Supports with Enhanced Stability ^†

Grape marc is a residue from the wine industry that contains a notable amount of polyphenols, which present antioxidant and anti-inflammatory properties [1]. Herein, we report the embedding of phenolic extract into mesoporous MCM-41-type silica matrices to enhance its stability with radical scavenger activity (RSA) preservation. As supports, pristine MCM-41 and mesoporous silica materials decorated with ZnO nanoparticles prepared by a reported procedure involving an ion exchange process between surfactant cations attached to the inner pore wall surfaces of silica and Zn²⁺ in a methanolic solution, which led to the formation of ZnO nanoparticles on silica surface during the material calcination [2]. As grape marc, Mamaia variety from Murfatlar (Romania) was used to prepare hydro-alcoholic phenolic extracts through conventional extraction (dry pomace marc weight/solvent = 1/6 w/v), which consisted of heating at reflux in three steps. The fractions from extraction were further analyzed separately and as overall extract.

The composition of polyphenolic extract was analyzed by reversed-phase high performance liquid chromatography with photometric diode array detector (HPLC-PDA) and spectrophotometric determination of total polyphenols (using Folin–Ciocalteu reagent), total flavonoids, and total anthocyanin monomeric pigments content. The radical scavenger activity (2,2-diphenyl-1-picrylhydrazyl-DPPH and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)-ABTS assays) of grape marc extracts was evaluated. Our recently reported method was used for RSA determination on solid samples by comparing the antioxidant activity of embedded extract with that of the corresponding support and extract (using the same amount as in the material containing embedded phytochemicals) [3]. The solid samples were characterized by FT-IR spectroscopy and nitrogen adsorption-desorption isotherms. The content of organic compounds into silica-type matrices was determined by thermal analysis (TG-DTA).

All supports presented high porosity and the ability to host a large amount of organic compounds (40–45% wt), making them suitable for extract encapsulation and the preservation of its beneficial effects.

The overall hydro-alcoholic extract from Mamaia grape pomace contained high polyphenolic content (27.50 ± 0.60 mg equivalent of gallic acid/g dry marc) and had a good antioxidant activity (264.55 ± 5.04 and 237.14 ± 5.47 g Trolox equivalent/g of extract determined by DPPH and ABTS assays, respectively).

The resulted materials obtained after the embedding of polyphenols showed an improved RSA in comparison to the corresponding extract, thus proving an enhanced stability, and hence preserving the beneficial effects of the phytochemicals. The toxicity of grape marc extract free and embedded in silica-type matrices was assessed on NIH 3T3 murine fibroblasts cell line. The proposed materials containing polyphenolic extract can be further used in the development of nutraceuticals.